Re: [PATCH] regulator: core: Resolve supply name earlier to prevent double-init

["Christian Kohlschütter" <christian@kohlschutter.com>]

Hi all,

This is a follow-up patch from my patch on mmc side:
[PATCH v4] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4
https://patchwork.kernel.org/project/linux-rockchip/patch/73F9AED0-D2A8-4294-B6E1-1B92D2A36529@kohlschutter.com/

Thanks to Robin Murphy's help, we were able to figure out that my NanoPI R4S's SD-Card voltage regulator was initialized twice and that a voltage drop was the reason for the initialization failure.
Adding an mdelay to the init code, or — surprisingly — adding a "regulator-uv-protection-microvolt" declaration had "fixed" the issue in 99/100 tries.

Best,
Christian

from arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi:
vcc3v0_sd: vcc3v0-sd {
        compatible = "regulator-fixed";
        enable-active-high;
        gpio = <&gpio0 RK_PA1 GPIO_ACTIVE_HIGH>;
        pinctrl-names = "default";
        pinctrl-0 = <&sdmmc0_pwr_h>;
        regulator-always-on;
        regulator-min-microvolt = <3000000>;
        regulator-max-microvolt = <3000000>;
        regulator-name = "vcc3v0_sd";
        vin-supply = <&vcc3v3_sys>;
};                                        

> Am 15.07.2022 um 22:32 schrieb Christian Kohlschütter <christian@kohlschutter.com>:
> 
> Previously, an unresolved regulator supply reference upon calling
> regulator_register on an always-on or boot-on regulator caused
> set_machine_constraints to be called twice.
> 
> This in turn may initialize the regulator twice, leading to voltage
> glitches that are timing-dependent. A simple, unrelated configuration
> change may be enough to hide this problem, only to be surfaced by
> chance.
> 
> One such example is the SD-Card voltage regulator in a NanoPI R4S that
> would not initialize reliably unless the registration flow was just
> complex enough to allow the regulator to properly reset between calls.
> 
> Fix this by re-arranging regulator_register, trying resolve the
> regulator's supply early enough that set_machine_constraints does not
> need to be called twice.
> 
> Signed-off-by: Christian Kohlschütter <christian@kohlschutter.com>
> ---
> drivers/regulator/core.c | 42 ++++++++++++++++++++++++++--------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index c4d844ffad7a..728840827e9c 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -5433,7 +5433,34 @@ regulator_register(const struct regulator_desc *regulator_desc,
> 	BLOCKING_INIT_NOTIFIER_HEAD(&rdev->notifier);
> 	INIT_DELAYED_WORK(&rdev->disable_work, regulator_disable_work);
> 
> -	/* preform any regulator specific init */
> +	/* set regulator constraints */
> +	if (init_data)
> +		rdev->constraints = kmemdup(&init_data->constraints,
> +					    sizeof(*rdev->constraints),
> +					    GFP_KERNEL);
> +	else
> +		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
> +					    GFP_KERNEL);
> +
> +	if (init_data && init_data->supply_regulator)
> +		rdev->supply_name = init_data->supply_regulator;
> +	else if (regulator_desc->supply_name)
> +		rdev->supply_name = regulator_desc->supply_name;
> +
> +	if ((rdev->supply_name && !rdev->supply) && rdev->constraints
> +		&& (rdev->constraints->always_on || rdev->constraints->boot_on)) {
> +		/* Try to resolve the name of the supplying regulator here first
> +		 * so we prevent double-initializing the regulator, which may
> +		 * cause timing-specific voltage brownouts/glitches that are
> +		 * hard to debug.
> +		 */
> +		ret = regulator_resolve_supply(rdev);
> +		if (ret)
> +			rdev_dbg(rdev, "unable to resolve supply early: %pe\n",
> +					 ERR_PTR(ret));
> +	}
> +
> +	/* perform any regulator specific init */
> 	if (init_data && init_data->regulator_init) {
> 		ret = init_data->regulator_init(rdev->reg_data);
> 		if (ret < 0)
> @@ -5459,24 +5486,11 @@ regulator_register(const struct regulator_desc *regulator_desc,
> 		    (unsigned long) atomic_inc_return(&regulator_no));
> 	dev_set_drvdata(&rdev->dev, rdev);
> 
> -	/* set regulator constraints */
> -	if (init_data)
> -		rdev->constraints = kmemdup(&init_data->constraints,
> -					    sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> -	else
> -		rdev->constraints = kzalloc(sizeof(*rdev->constraints),
> -					    GFP_KERNEL);
> 	if (!rdev->constraints) {
> 		ret = -ENOMEM;
> 		goto wash;
> 	}
> 
> -	if (init_data && init_data->supply_regulator)
> -		rdev->supply_name = init_data->supply_regulator;
> -	else if (regulator_desc->supply_name)
> -		rdev->supply_name = regulator_desc->supply_name;
> -
> 	ret = set_machine_constraints(rdev);
> 	if (ret == -EPROBE_DEFER) {
> 		/* Regulator might be in bypass mode and so needs its supply
> -- 
> 2.36.1
>